package com.freetymekiyan.algorithms.level.medium;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;

/**
 * 380. Insert Delete GetRandom O(1)
 * <p>
 * Design a data structure that supports all following operations in average O(1) time.
 * <p>
 * insert(val): Inserts an item val to the set if not already present.
 * remove(val): Removes an item val from the set if present.
 * getRandom: Returns a random element from current set of elements. Each element must have the same probability of
 * being returned.
 * Example:
 * <p>
 * // Init an empty set.
 * RandomizedSet randomSet = new RandomizedSet();
 * <p>
 * // Inserts 1 to the set. Returns true as 1 was inserted successfully.
 * randomSet.insert(1);
 * <p>
 * // Returns false as 2 does not exist in the set.
 * randomSet.remove(2);
 * <p>
 * // Inserts 2 to the set, returns true. Set now contains [1,2].
 * randomSet.insert(2);
 * <p>
 * // getRandom should return either 1 or 2 randomly.
 * randomSet.getRandom();
 * <p>
 * // Removes 1 from the set, returns true. Set now contains [2].
 * randomSet.remove(1);
 * <p>
 * // 2 was already in the set, so return false.
 * randomSet.insert(2);
 * <p>
 * // Since 2 is the only number in the set, getRandom always return 2.
 * randomSet.getRandom();
 * <p>
 * Related Topics: Array, Hash Table, Design
 * Similar Questions: (H) Insert Delete GetRandom O(1) - Duplicates allowed
 */
public class InsertDeleteGetRandom {

  /**
   * Your RandomizedSet object will be instantiated and called as such:
   * RandomizedSet obj = new RandomizedSet();
   * boolean param_1 = obj.insert(val);
   * boolean param_2 = obj.remove(val);
   * int param_3 = obj.getRandom();
   */
  class RandomizedSet {

    private List<Integer> nums;
    private Map<Integer, Integer> numToIndex;
    private Random r;

    /**
     * Initialize your data structure here.
     */
    public RandomizedSet() {
      nums = new ArrayList<>();
      numToIndex = new HashMap<>();
      r = new Random();
    }

    /**
     * Inserts a value to the set. Returns true if the set did not already contain the specified element.
     * Check if the value exists.
     * If yes, return false.
     * If not, insert the value to the list.
     * Then put the <num, index> to the map.
     * Return true.
     */
    public boolean insert(int val) {
      if (numToIndex.containsKey(val)) return false;
      nums.add(val);
      numToIndex.put(val, nums.size() - 1);
      return true;
    }

    /**
     * Removes a value from the set. Returns true if the set contained the specified element.
     * Check if the value exists.
     * If not, nothing to remove, return false.
     * If yes, we try to remove it.
     * If we remove it directly from where it is, we will have to update all the numbers after it in the list.
     * To avoid that, we swap it with the last number. Then we won't need to update a bunch of numbers.
     * So get its index, get the last number, put the last number to the position.
     * Then remove the val from the list and map.
     */
    public boolean remove(int val) {
      if (!numToIndex.containsKey(val)) return false;
      int index = numToIndex.get(val);
      int lastNum = nums.get(nums.size() - 1);
      numToIndex.put(lastNum, index);
      nums.set(index, lastNum);
      nums.remove(nums.size() - 1);
      numToIndex.remove(val);
      return true;
    }

    /**
     * Get a random element from the set.
     * Just generate a random index.
     */
    public int getRandom() {
      return nums.get(r.nextInt(nums.size()));
    }
  }
}